The present invention relates to thermostatic switch assemblies of the type employing a temperature responsive element operative to effect actuation and deactuation of an electrical switch for controlling current flow to a load circuit.
Thermostatic assemblies of the aforesaid type are often employed for controlling current flow to a compressor motor for a stationary refrigeration or air conditioning system and in vehicular applications to control current flow to the compressor clutch where the clutch is driven by a power transmission connected to the vehicle engine.
Thermostatic switch assemblies typically employ a temperature responsive member such as a fluid filled capsule having a movable diaphragm-wall portion or a bimetal element which moves upon experiencing changes in the sensed temperature. In refrigeration control systems either stationary or vehicular, it is desired to sense the temperature of the refrigerant flowing at certain locations in the circuit such as for example, at the evaporator and to effect cycling of the compressor in response to preselected sensed temperatures.
Thermostatic switch assemblies of the aforesaid mechanical type have been proven inexpensive to manufacture in high volume and reliable over extended periods of operation in the environments to which refrigeration systems are subjected.
However, in certain applications such as automotive air conditioning systems it has been desired to provide for a change of mode of operation in which the compressor clutch is cycled. It has been desired to maintain the refrigerant in the evaporator at slightly higher values in order to shorten the compressor duty cycle and effect economy of operation of the vehicle, inasmuch as the additional load of the compressor is applied to the engine for minimum time periods in order to effect a satisfactory level of passenger compartment comfort. It has been also desired to provide a "Maximum Cool Down" mode of operation for a vehicle air conditioning system and particularly where the vehicle has been sitting in the sun for extended periods of time and the passenger compartment is at intolerable elevated temperature levels upon initial entry of the passengers.
If the temperature settings for the compressor cycling are established at values to maintain the evaporator at the lowest permissible temperature for effecting maximum cooling of the passenger compartment, the compressor will cycle for unnecessarily long periods of time in order to maintain the evaporator at a minimum temperature for fastest cooling.
Accordingly it has been desired to provide a vehicle air conditioning system in which the system could be initially operated for cooling the evaporator to the minimum temperature permissible without causing freezing and ice formation on the surface of the evaporator, to provide Maximum Cool Down. It has further been desired to enable the system to be later switched by the user or vehicle operator to a mode of operation wherein a lesser amount of cooling is employed to thereafter maintain the passenger compartment at a desired comfort level.
However, in the past where mechanical temperature sensing or pressure sensors have been employed at the evaporator to determine refrigerant temperature, in order to provide a dual mode of operation it has been necessary to provide separate sensors having different temperature settings and to switch between sensors. Therefore, it has been desired to provide a refrigeration system and particularly an automotive vehicle air conditioning system wherein reliable mechanical temperature sensing means are employed for monitoring evaporator temperature to actuate and deactuate a switch for cycling the electrical compressor drive clutch and to provide remote changing of the cycling temperatures for the compressor and yet maintain the reliability of the mechanical temperature sensing devices.
However, it has not been known how to remotely change the temperature setting of a mechanical temperature sensor or thermostat once installed in the system. It has been particularly desired to find a way to remotely control the thermostat when located on the evaporator or on the suction return line in the engine compartment of the vehicle.